1. Field of the Invention
This invention relates to a device for diagnosing trouble in ignition devices which have a longer electrical discharge time than ordinary ignition devices.
2. Description of the Prior Art
In recent years, ignition devices with long electrical discharge times, such as the device shown in FIG. 1, have been used with the aim of improving fuel efficiency and acceleration in vehicles.
In FIG. 1, an ignition coil 1 and a transistor 2 which is used for driving the spark coil are the same as in an ordinary ignition device. The control circuit 3, which comprises an oscillator and a monostable multivibrator, is connected so that it receives the signal A, which has the voltage waveform shown in FIG. 2a and is generated from the ignition signal at the primary side of the ignition coil 1, as input, and outputs the square wave signal B shown in FIG. 2b. A transformer 4, which includes a forward resonant-type DC/DC converter and a high-voltage diode used for half-wave rectification, is driven by a power transistor 5 driven by the output of the above-mentioned control circuit 3. In a previously existing type of ignition system, it is possible to lengthen the electrical discharge time by adding the above-mentioned control circuit 3, transformer 4 and power transistor 5, so that the signal C which is generated on the secondary side of the ignition coil 1, that is to say the secondary current of the ignition coil, becomes as is shown by the solid line in FIG. 2c. The dotted line in FIG. 2c shows the secondary current waveform without the added components.
However, when the electrical discharge time of the ignition device is lengthened as described above, even if trouble develops in the control circuit 3, transformer 4 or power transistor 5, so that the lengthening of the electrical discharge time is not performed (such a discharge is to be referred to below as a discharge), a prior art ignition system will continue to ignite and the engine will continue to run, so that it is difficult to detect the trouble.